Process and apparatus for preparing pigment flush

ABSTRACT

The present invention provides a process for continuous production of pigment flushes and an apparatus for carrying out the process. In the process of the invention, the pigment press cake is first fluidized. The fluidized press cake and a hydrophobic liquid organic medium are fed into a twin screw extruder. The kneading of the organic medium and press cake between the twin screws flushes the pigment into the organic medium. The water phase and flushed pigment phase are separated by removing at least part of the water phase through a vent in the extruder. An impediment to the flow of material downstream of the water vent causes the flush to accumulate in the vented section for a period of time sufficient to remove the desired amount of the water phase. The flush works over the impediment and passes downstream to where vacuum is applied to remove residual water from the flush. The flush may be further combined with other ink ingredients to form an ink product.

This is a divisional of application Ser. No. 09/397,801, filed Sep. 17,1999.

FIELD OF THE INVENTION

The present invention relates to processes for preparing pigmentflushes, particularly pigment flushes for ink compositions. The presentinvention also relates to methods for preparing ink bases and finishedink compositions.

BACKGROUND OF THE INVENTION

Syntheses of many organic pigments include a coupling step in a diluteaqueous medium to produce a slurry of the pigment product, which istypically followed by filtering the slurry in a filter press toconcentrate the pigment. The press cake that results is then eitherdried to provide a dry, particulate pigment or else is “flushed” with anorganic medium such as an oil and/or resin to transfer the pigmentparticles from the aqueous press cake to the oil or resin phase.Flushing assists in keeping pigment particles non-agglomerated andeasier to use in making inks or coatings. The flushing process requiresadditional time and materials over simply drying the pigment. If thepigment is used in an ink or coating composition, however, it must firstbe well-dispersed in an appropriate organic medium in order to achievethe desired color development and stability, and thus the flushingprocess is advantageous because it accomplishes the transfer withoutintermediate steps of drying the pigment and grinding the pigment in theorganic medium to produce the pigment dispersion.

In the past, pigment flushes have usually been prepared by batchprocesses in which the press cake is kneaded with an organic phase suchas an oil and/or a resin, for example in a sigma blade mixer or doughmixer, to flush the pigment particles from the water phase to theorganic medium phase and displace the water as a separate aqueous phase.The displaced water is separated and the dispersion of the pigment inthe varnish can be used as a pigment paste in preparing an ink or paint.

The batch process has many shortcomings. First, the steps of addingvarnish, kneading the dough to displace the water, and pouring off thewater must usually be repeated a number of times in order to obtain theoptimum yield and a product with the desired low water content. This isa labor-intensive process that requires careful monitoring. Further, inorder to remove the residual water, the batch must be further treated,such as by heating and stripping under vacuum. For many pigments, theheat history from processing to remove the residual water may result ina color shift. Further, the process is time-consuming and inefficient.Finally, it is difficult to reduce the water content below about 3% byweight, even with the vacuum stripping.

Continuous flush processes have been suggested in the past, but thoseprocesses have also had shortcomings. Higuchi et al., U.S. Pat. No.4,474,473, describe a process for continuously flushing pigment presscake on equipment that includes a co-rotating, twin screw extruder. Theprocess requires a press cake that has a pigment content of 35 weightpercent or more. The '473 patent discloses that press cakes having apigment content of from 15 to 35 weight percent cannot be used in thecontinuous process because of problems with obtaining constant flowfeeding. The range of 15 to 35 weight percent, however, is the range ofpigment content that is typically obtained for press cakes. Whiledilution of the press cake with water to form a liquid slurry of lowpigment content was previously suggested, the '473 patent takes theopposite direction of increasing pigment content to 35% or more toprovide a “lump cake” that is apparently suitable for constant flowfeeding as a free-flowing solid. Increasing the pigment content of themanufactured press cake, however, requires a time-consuming process ofshaping the press cake and drying it with circulating air until thedesired water content is obtained.

An example of the methods using diluted press cake is Rouwhorst et al.,U.S. Pat. No. 4,309,223. This patent discloses a process of preparing apigment flush from a press cake using a single screw extruder. Theprocess uses a slurry containing only about 0.5% to 10% by weightpigment. When so much water is added during the flushing process it isdifficult to get a clean break or separation between the phases. Inaddition, more aqueous waste is produced. Finally, it is often the casethat the single screw extruder does not provide a sufficient amount ofmixing shear to adequately flush the press cake.

Anderson et al., U.S. Pat. No. 5,151,026, discloses an extruderapparatus for removing liquid from an aqueous mass of comminuted solidssuch as crumb rubber, wood pulp, and ground plastic materials that arecleansed during recycling processes. The water is squeezed out of theaqueous mass in a pinch point. The pinch point pressure results fromapplying a backward force by means of a reverse-threaded section of thescrew immediately at the liquid extraction location. The Andersonprocess removes from water relatively large solid pieces that do notappear to associate or agglomerate. Unlike the Anderson process, thepigment flush process concerns transfer of fine pigment particles fromaqueous press cake to an organic phase, usually including a resin,followed by separation of the two liquid phases (aqueous and organic).Two key considerations in the flush process are clean separation of theorganic and aqueous phases and good dispersion of the pigment particles.The pinch point method is unsuitable for the two-phase pigment flushingprocess because the pinching force would interfere with the necessaryphase separation between aqueous and organic phases. The pigmentparticles also have a tendency to agglomerate. The pinch point wouldthus be unsuitable for the additional reason that squeezing the pigmentwould cause undesirable agglomeration of the pigment particles, whichwould in turn impair dispersion of the pigment.

SUMMARY OF THE INVENTION

The invention provides a process for continuous production of pigmentflush from conventional press cake. In a first step, at least onepigment press cake is homogenized to a fluidized mass. In a second step,the homogenized press cake is fed at a controlled rate into a twin screwextruder. The twin screw extruder may receive more than one stream offluidized press cake. An organic medium, which may include organiccomponents selected from solvent, varnish, oil, and/or resin, is alsofed into the extruder, and the press cake and organic medium are mixedin a first zone of the extruder to wet the pigment with the organicmedium, displacing water from the press cake and producing a crudepigment flush. The displaced water is removed in a second zone of theextruder. The second zone of the extruder includes a port for removingthe displaced water, especially by draining the water, and preferablyincludes a dam that retains the pigment flush in the second zone for atime sufficient to allow most of the displaced water to be removed fromthe crude flush mass. The extruder preferably includes a third zone thathas one or more vacuum ports to draw off residual water clinging to thepigment flush.

The invention also provides a method for continuous production of an inkbase or a finished ink from a pigment press cake. The method includesthe steps just outlined for the process of the invention for producing apigment flush and at least one an additional step of introducing intothe extruder, at some point before the pigment dispersion is discharged,preferably after the optional vacuum zone, one or more additional inkcomponents, such as a varnish, pigmented tinting or toning compositions,solvent, and/or additives, to make an ink base or a finished inkcomposition.

The invention further provides an apparatus that includes a press cakefeed system and a twin screw extruder. The press cake feed system isused to fluidize the press cake and feed the fluidized press cake to theextruder. The press cake feed system applies shear to the press cake toconvert the crumbly, agglomerating material into a smooth, fluiddispersion. The feed system then transfers the fluidized press cake tothe twin screw extruder. The twin screw extruder of the apparatus has atleast two zones. In a first zone, the fluidized press cake and anorganic medium are fed into the extruder and mixed. The action of thefirst zone transfers the pigment to the organic medium and produces aseparate water phase. In a second zone of the extruder, the water phaseis at least partially removed. In an optional third zone, a residualportion of water is removed from the pigment flush by vacuum. Theextruder may also optionally have a fourth zone with at least oneaddition port by which additional ingredients are added and whichprovides additional mixing to prepare an ink base or finished inkcomposition.

The invention offers an advantage over previous processes in that itprovides continuous processing of conventional press cakes. Press cakesare usually prepared having pigment contents of from about 15% to about35%. Because the present invention can process press cakes as prepared,it is possible to eliminate a cumbersome preliminary evaporation step toincrease pigment content of the press cake to the point at which thepress cake can be flushed or a diluting step in which the press cake isreduced to a very low solids slurry for processing using the prior artmethods.

The invention offers a further advantage of providing more control for acontinuous flushing process, which results in increased consistency ofcolor and other properties of the pigment dispersion.

The invention offers a still further advantage of providing a continuousprocess for manufacturing ink base or a finished ink product from acontinuous feed of conventional press cake.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of one embodiment of the press cake feedsystem of the invention.

FIG. 2 is a schematic diagram of an alternative embodiment of the presscake feed system of the invention.

FIG. 3 is a schematic diagram of one embodiment of the twin screwextruder of the present invention.

FIG. 4 is a partial schematic view of the water separation zone of theinvention.

FIG. 5 is a partial schematic view of an alternative embodiment of theextruder showing the fourth zone.

DETAILED DESCRIPTION

The invention provides a process in which a pigment in press cake formis flushed by transferring the pigment particles from the aqueous presscake to an organic medium, especially to an oil or resin phase. Thepress cake may be from the synthesis of any of a number of organicpigments. Examples of suitable press cakes include, without limitation,press cakes of diarrylide yellow pigments e.g., Pigment Yellow 12),phthalocyanine pigments, calcium lithol red, alkali blue, barium litholred, rhodamine yellow, rhodamine blue, and so on. Press cakes of organicpigments typically have a water content by weight of from about 12% toabout 30%, although press cakes such as those of certain blue pigmentsmay have a water content as high as 45%.

The invention further provides an apparatus that includes at least onepress cake feed system, a preferred embodiment of which is shown in FIG.1, and a twin screw extruder, a preferred embodiment of which is shownin FIG. 3. The press cake feed system fluidizes the press cake and feedsthe fluidized press cake to the twin screw extruder. The press cake feedsystem may include two components that carry out these actions, afluidizing component such as 1 in FIG. 1 and a feed component such as 2in FIG. 1. The fluidizing component applies shear to the press cake tobreak up the bridging between the individual particles that gives thepress cake its pasty or plaster-like consistency. The amount of shear issufficient to produce a fluidized press cake. The amount of shear shouldnot be excessive, as too much shear will beat air into the fluidizedpress cake, making it difficult again to feed into the extruder.Suitable examples of the fluidizing component are, without limitation, aribbon mixer, a paddle mixer, an auger screw, and a helical mixer. FIG.1 shows as one preferred embodiment of the fluidizing component a paddlemixer 3 driven by motor 13. Paddle mixer 3 shows ten paddle mixingelements 4, but the size of the paddle mixer and the number of mixingelements can be varied widely to suit the particular situation, such asthe desired throughput of the continuous process. Scrapers 10 may beincluded to scrape the walls and keep the press cake inside the mixer.If necessary, the mixer may be cooled with the aid of a cooling jacket(not shown), by air cooling, or otherwise.

The fluidizing component has a orifice 5 through which the fluidizedpress cake exits the fluidizing component. The fluidized press cake maybe discharged from the fluidizing component by pushing the fluidizedpress cake through the orifice with a valve 6, as is shown in FIG. 1, tocontrol the flow of fluidized press cake from the fluidizing component.Alternatively, the fluidized press cake may be drawn from the fluidizingcomponent with vacuum or pumped from the fluidizing component. In apreferred embodiment, the fluidized press cake is fed into a holdingtank 7 as shown in FIG. 1. Holding tank 7 is equipped with a blade 8that rotates along the perimeter and serves both to prevent re-bridgingbetween the pigment particles of the fluidized press cake and to aid infeeding the press cake to feed pump 9. Feed pump 9 provides fluidizedpress cake to the extruder. Holding tank 7 allows the fluidizingoperation taking place in paddle mixer 3 to be carried out in a batch orsemi-batch manner, with all or part of the fluidized press cake in themixer being emptied to the holding tank at intervals. Thus, press cakecan be fluidized in a batch method with a portion of press cake beingintroduced to the mixer, mixed until fluidized, then the fluidizedportion passed on to the holding tank. The mixer may then be chargedwith a new batch of press cake, which is fluidized. The fluidized presscake may be immediately introduced to the holding tank or held in themixer for a desired time and then introduced to the holding tank.Alternatively, a semi-batch process may be employed in which at certainintervals a part of the fluidized press cake is passed from the mixer tothe holding tank, after which additional press cake is added to thematerial remaining in the mixer.

It is also possible to forego the holding tank in the press cakefluidizing component. In this embodiment (not shown), the fluidizedpress cake is passed at a continuous rate from the mixer through thepump to the extruder. In this embodiment of the invention, new presscake is fed into the mixer at a rate sufficient to insure that the mixerdoes not empty and that the average dwell time of the press cake in themixer is adequate to fluidize the press cake.

The feed component of the press cake feed system feeds the fluidizedpress cake to the extruder. Preferably, the feed component includes apump. The pump may be any type suitable for the viscosity of thefluidized press cake. Examples of suitable pumps include, withoutlimitation, lobe pumps, gear pumps, or other positive displacementpumps.

In the alternative preferred embodiment shown in FIG. 2, the press cakefeed system has a fluidizing component that includes a conical container101 that preferably rotates by gear 102 driven by motor 111 and astationary two-screw auger 103 (front screw shown) with motor 113 thatapplies shear to the press cake. The press cake is fluidized by theaction of the two-screw auger. The auger also serves to convey thefluidized press cake to an orifice 105 at the bottom of the conicalcontainer. The fluidized press cake expelled from the orifice is fed tothe extruder, again for example by pump 109, with or without a holdingtank for the fluidized material, as in the first embodiment.

The feed component introduces the fluidized press cake to port 19 at thebeginning of an extruder shown in the preferred example of FIG. 3. Theextruder has at least two zones, and optionally has a third and/or afourth zone. In a first zone, represented in the figure by sections 1through 5, the fluidized press cake and organic medium are fed into theextruder and then mixed to flush the pigment from the aqueous phase tothe organic phase. In a second zone, represented by sections 6 through8, at least a portion the water displaced during the flushing operationis removed by draining or drawing the liquid from the extruder. In athird zone, which is optional but preferred, represented by sections 9through 11, residual water is removed (as water vapor) by vacuumdehydrating the pigment flush through one or more vacuum ports. In thefourth zone, also optional, represented by sections 12 through 14, theflush is further mixed and one or more other ink components may be addedand mixed with the pigment flush. The optional fourth zone can be usedto produce an ink base or finished ink composition product.

The extruder is a twin-screw extruder, with the screws being driven bymotor 18. The screws are preferably co-rotating. At least one fluidizedpress cake is fed into the extruder through port 19. In one preferredembodiment, a second fluidized press cake is fed into the extruderthrough a port 19 or through a second port 119. A liquid organic medium,preferably including at least an oil, a resin, or resin solution, isalso fed into the extruder, which may be through port 19 or through asecond port 119. The liquid organic medium is sufficiently hydrophobicto allow a non-aqueous phase to form in the process. Types of organicmaterials that are suitable to prepare pigment are well-known in theart. If the extruder has two different fluidized press cake feeds byports 19 and 119, the organic medium may be fed through either orthrough yet another separate port.

Typical kinds of resins and oils that may be used for flushing varnishesinclude, without limitation, alkyd resins, phenolic resins, polyesters,hydrocarbon resins, maleic resins, rosin-modified varnishes of any ofthese, polyamide resins, polyvinyl chloride resins, vinyl acetateresins, vinyl chloride/vinyl acetate copolymer resins, chlorinatedpolyolefins, polystyrene resins, acrylic resins, polyurethane resins,ketone resins, vegetable oils including linseed oil, soybean oil,neatsfoot oil, coconut oil, tung oil, mineral oils, and so on.Combinations of such resins and oils may also be employed. The resin,oil, or combination thereof may be combined with a hydrophobic organicsolvent or liquid, including high boiling petroleum distillates.

As mentioned, the organic medium may be introduced in the same barrel,or section, of the extruder as the fluidized press cake, whether in thesame port or a different port. Alternatively, the organic medium may beintroduced in another section close to the front of the extruder in thefirst zone, as shown in FIG. 3 by the port 119. The organic medium maybe fed from a line or tank, which may have a stirrer, and may be meteredin with, for example, a pump. Preferably, the organic medium and thefluidized press cake are each introduced at fairly constant rates. Therelative amounts of the organic medium and the fluidized press cake foroptimum processing can be determined based upon the particular materialschosen, but in general the amounts remain the same as those expected forconventional batch processing. For example, the amount of organic mediumintroduced per unit of time may be from about 0.6 to about 2 times theamount of solid pigment introduced in the same unit of time. The ratioof organic medium to solid pigment may be adjusted according to factorsknown in the art, such as the type of pigment and the type of organicmedium.

The fluidized press cake and organic medium are mixed in one or moresections of the first zone of the extruder to wet the pigment with theorganic medium, displacing water from the press cake and producing acrude pigment flush. A special screw section with a plurality ofkneading disks may be used in the first zone where the flushing takesplace. In one preferred embodiment of the invention, the screw profilein the first zone tapers from a deep channel used in the section orsections having a feeding port gradually to a shallow channel in a later(downstream) section or section of the first zone. The length of thefirst zone of the extruder in which the fluidized press cake and theorganic medium are mixed is sufficiently long so that the pigment isflushed completely. The rotational speed of the screw also is a factorfor efficient flushing. A preferred range for rotational speed of thescrew is from about 150 to about 550 rpm, and a more preferred range forrotational speed is from about 450 to about 550 rpm.

The displaced water and the crude pigment flush continue in the extruderto the second zone of the extruder where at least a portion of thedisplaced water is removed. In the second zone, preferably a majorportion of the is placed water is removed, more preferably at leastabout 80%, still more preferably at least about 90%, and even morepreferably all but a residual amount of water that clings to the pigmentflush is removed. Referring to FIG. 3, the second zone of the extruderincludes sections 6-8. The second zone of the extruder includes a portor vent 20 for removing, preferably by draining off, the displacedwater. While the water may be withdrawn by other means, gravity drainingis the simplest and is therefore preferred. The port 20 shown in thefigure is connected on the other side to a section 21 having therein ascrew turned by motor 22 that drives the relatively viscouspigment-containing flush back into the section 6 while letting the waterdrain out of section 6. Collected water is drained via valve 23.

One important feature of the second zone is a dam that retains thepigment flush for a time sufficient to allow most of the displaced waterto drain from the crude flush mass. The dam causes the kneaded presscake/organic medium to dwell over the port long enough to allow more ofthe displaced water to drain from the kneaded pigment. A portion of themixture of press cake and organic medium is carried into the dammedsection of the extruder and remains in that section until the portionworks its way out of the pocket of retained material and is carried intothe next section by the grabbing action of the screw. The dam is shownin more detail in FIG. 4. FIG. 4 shows the screw sections in sections 6to 8 of the second zone. The features of section 6 are the port 20, sidesection 21 (shown in part) containing screw 121, and screw section 130.Screw section 130 has relatively tight threads to remove material fromthe mixing zone. Screw sections 131 and 132 in marked barrels 6 and 7 ahave threads that are less tight to increase residence time and allowopen room for water to drain. The screw sections designated by 133 arereverse threaded in a tight thread to provide sufficient reverse flow tocause the material to fill a section of 7 a (for example, about 30 mm).The reverse flow force that causes the damming effect is limited so thatthere is no squeezing, as squeezing would tend to produce an emulsion ofthe aqueous and organic phases, impairing the desired separation ofwater from organic phase. Because the draining port 20 is relatively farupstream from the reverse screws, the effect of the reverse flow is tocause material to accumulate before eventually flowing over the createddam and/or being pulled on by forward-tuming screws located furtherdownstream. The water is not engaged by the forward screws and does notflow over the accumulated material. Instead, the water is held in thesecond zone to drain.

Because more of the water is drained from the flush in a liquid phaseinstead of being evaporated, as compared to prior methods, the finalproduct contains a lower concentration of salts. The dam thus improvesthe purity of the product.

The third zone of the extruder, which is optional but preferred,includes one or more vacuum ports 24 connected to vacuum at valves 25 todraw off residual water clinging to the pigment flush. The water isdrawn off as water vapor. Suitable vacuum ports are known to be usedwith extruders and typically can include a section 26 containing a screwturned by motor 27 in the vacuum port to help retain the flush in theextruder. A vacuum pump is typically connected to the vacuum port toprovide the reduced pressure. The profile of the screw used for thevacuum section preferably has a shallow channel, which tends to increasethe efficiency of vacuum dehydration by shaping the material in a thinlayer form. FIG. 3 shows identical vacuum ports on consecutive extrudersections.

The present process is particularly advantageous for preparing flushesof pigments that are heat-sensitive, including, without limitation,diarrylide and rhodamine pigments such as diarrylide yellow, rhodamineyellow, and rhodamine blue. Because the time during which the pigment isexposed to higher temperatures is minimized by the process of theinvention, pigments that may discolor when exposed to heat may be mademore reproducibly and without significant color degradation.

The pigment flush produced by the inventive process may be used toprepare an ink composition according to usual methods. Additionalresins, oils, solvents or other components of the organic medium may beadded after the vacuum port to adjust the composition of the pigmentflush. FIG. 5 shows an alternative fourth zone having ports 130 and 131for addition of one or more further materials.

Alternatively, the pigment flush may be made into an ink base or afinished ink composition as a further step of the continuous process ofthe invention by introducing additional materials such as varnish, otherresins, organic solvent and/or additives into the extruder at some pointbefore the pigment flush is discharged, preferably after the vacuumzone, such as into port 130 or port 131. The flushed pigment dispersionand other ink component(s) are combined in the extruder so that theoutput from the extruder is an ink base or ink composition. Typicalresins used as ink varnishes that may be added include, withoutlimitation, alkyd resins, polyesters, phenolic resins, rosins,cellulosics, and derivatives of these such as rosin-modified phenolics,phenolic-modified rosins, hydrocarbon-modified rosins, maleic modifiedrosin, fumaric modified rosins; hydrocarbon resins, vinyl resinsincluding acrylic resins, polyvinyl chloride resins, vinyl acetateresins, polystyrene, and copolymers thereof; polyurethanes, polyamideresins, and so on. Combinations of such resins may also be employed.Suitable example of organic solvents that may be added include, withoutlimitation, aliphatic hydrocarbons such as petroleum distillatefractions and normal and isoparaffinic solvents with limited aromaticcharacter. Any of the many additives known in the art that may beincluded in the ink compositions of the invention, so long as suchadditives do not significantly detract from the benefits of the presentinvention. Illustrative examples of these include, without limitation,pour point depressants, surfactants, wetting agents, waxes, emulsifyingagents and dispersing agents, defoamers, antioxidants, UV absorbers,dryers (e.g., for formulations containing vegetable oils), flow agentsand other rheology modifiers, gloss enhancers, and anti-settling agents.When included, additives are typically included in amounts of at leastabout 0.001% of the ink composition, and the additives may be includedin amounts of up to about 7% by weight or more of the ink composition.

The invention is illustrated by the following example. The example ismerely illustrative and does not in any way limit the scope of theinvention as described and claimed. All parts are parts by weight unlessotherwise noted.

EXAMPLE OF THE INVENTION

A twin screw co-rotating extruder with a screw diameter of 44 mm, L/D of56, and a speed of 450 rpm was used to produce the pigment flush. Thetable below summarizes the addition points, rates and temperatures ofthe extruder depicted in FIG. 3.

Bar- rels 1 2 3-5 6-8 7b-11 12 13 14 Func- add add mix- water vacu- mix-let mix- tion ing break um ing down ing dehy- dra- tion Feed wet varnish— — — — varnish — cake, and oil alkyd Jack- none heat heat heat heatheat cool cool et Temp — — 210 — 215 260 — 140 F. F. F. F.

First, a 22% lithol rubine press cake was fluidized to a homogenousmixture in a 5 hp ribbon mixer. After mixing, the fluidized press cakewas put into a feeder (a 25 hp helical mixer). The fluidized press cakewas fed at 124 lbs/hr using a gear pump, through a mass flow meter andinto barrel 1. The alkyd varnish was feed at 7 lbs/hr into barrel 1using a gear pump. A first hydrocarbon varnish was charged into barrel 2at 29 lbs/hr. This mass was then mixed through the end of barrel 5.

The water was drained from the pigment/vamish mass in barrels 6-8. Thewater was fairly clear and exited at 210° F. Barrels 7 b-11 were thevacuum dehydration zone. Vacuum ports were installed at barrels 9 and11.

The flush was further mixed in Section 12. In Section 13, the pigmentflush was reduced by addition of 11 lbs/hr of a hydrocarbon varnish and3.3 lbs/hr of a hydrocarbon oil and allowed to cool. The pigment flush,hydrocarbon varnish and hydrocarbon oil were further mixed and cooled inSection 14. The resulting product was a shade converted flush with lessthan 2% water content.

The invention has been described in detail with reference to preferredembodiments thereof. It should be understood, however, that variationsand modifications can be made within the spirit and scope of theinvention and of the following claims.

What is claimed is:
 1. An apparatus, comprising a press cake feedsystem, wherein said press cake feed system includes a shear componentfor fluidizing a press cake and a feed component for feeding thefluidized press cake; a source of organic medium; a twin screw extruderconnected to the feed component, wherein said twin screw extruderincludes a first zone with a port that receives the fluidized press cakefrom the feed component and mixes the fluidized press cake with theorganic medium; and a second zone downstream of the first zonecomprising an outlet for at least partially removing the water phase. 2.An apparatus according to claim 1, wherein said extruder furtherincludes a third zone downstream of the second zone comprising at leastone vacuum port.
 3. An apparatus according to claim 2, wherein the twinscrew extruder further comprises a fourth zone downstream of the thirdzone that includes at least one addition port.
 4. An apparatus accordingto claim 1, wherein said second zone comprises a partial dam thatimpedes the progress of the pigment flush out of the second zone for adesired time.
 5. An apparatus according to claim 4, wherein said partialdam comprises a reverse threaded screw section.
 6. An apparatusaccording to claim 1, wherein said first zone includes a plurality ofkneading disks.
 7. An apparatus according to claim 1, wherein theapparatus includes more than one press cake feed systems, eachconnecting to a port in the first zone.
 8. An apparatus according toclaim 7, wherein each press cake feed system connects to the same portin the first zone.
 9. An apparatus according to claim 7, wherein eachpress cake feed system connects to a different port in the first zone.10. An apparatus according to claim 1, wherein the press cake feedsystem further comprises a reservoir for maintaining the fluidized presscake upstream of the feed component.